This invention relates to test equipment for simulating vibration and shock loads applied to an article under test, and more particularly, to a vibration test fixture having a linear bearing system with large oil film bearing surfaces for supporting the load of a vibrating test article during single-axis vibration and shock testing.
The vibration test industry has adopted various methods and systems to simulate vibration and shock environments in order to determine product effectiveness and longevity when subjected to these environmental extremes. A parameter important to control in vibration and shock test equipment is the axis of vibration. Certain test equipment will produce single-axis vibration of the article under test, while restraining any cross-axis vibration or motion which is not along the input axis of the vibration source.
Various types of oil film tables, bearings, bearing oil film table combinations, and flexure guidance systems were developed to support the test articles during vibration testing. Early vibration restraint systems included hydrostatic journal bearing slip tables which included a number of drawbacks. To address these drawbacks, Applicant developed a vibration test fixture having a slip plate to which a single-axis reciprocating motion was applied for vibration or shock testing of an article carried on the moving slip plate as disclosed in U.S. Pat. No. 4,996,881. A linear bearing supports the load of the slip plate and the test object during reciprocating motion of the slip plate. The linear bearing has a generally planar, two-dimensional bearing surface for supporting the load while restraining cross-axis motion laterally and vertically with respect to the axis of motion. The entire load-supporting two-dimensional bearing surface area is lubricated with a thin film of oil, and the areas of multiple-axis restraint within the bearing also are lubricated with a thin film of oil during single-axis reciprocating motion of the slip plate. The linear bearing system provided a means of bearing support for the entire load of the slip plate and the test article on a constantly lubricated flat bearing surface during single-axis vibration, while also providing a constantly lubricated multiple-axis restraint means for the moving slip plate during testing.
The bearing system included an inverted T-shaped bearing guide member for mounting the slip plate for single-axis travel relative to the linear bearing support surface. The inverted T-shaped bearing guide member, combined with the oil film slip surfaces, provides a load capacity which exceeds the capacity of a standard high pressure journal bearing slip table system. The bearing system provided four oil ports on the top surface of the top plate to supply the oil for the T-film bearing. Such a design provided for a limited load capacity and tolerance for non-uniform external loads on the slip table. This design had an additional drawback in that deformation was created by temperature changes and temperature gradients which was a common condition when such T-film bearings were used with slip tables that were operated with thermal chambers. Consequently, a need exists for an improved vibration test fixture incorporating a T-film bearing in combination with a slip plate which addresses the drawbacks associated with prior designs.